The major objective of this project is to examine the mechanisms of action of chemotherapeutic agents and diets used in treatment of hyperlipoproteinemias. These hypolipidemic agents will be studied singly and in combination for their effectiveness in decreasing plasma lipoproteins, for the mechanisms by which they affect lipid and lipoprotein metabolism, and for the possibility that they also reduce tissue concentration of cholesterol. Also, specific attention will be given to possible short and long term side effects which may result from their use in patients with hyperlipidemia. Methods for this project will be those currently used in our laboratory for study of metabolism of sterols and lipoproteins. Studies will be carried out on a metabolic ward in patients with hyperlipidemia. The following measurements will be made in control periods and during treatment with various hypolipidemic agents: cholesterol synthesis, pool size, and absorption; bile acid pool sizes; biliary lipid composition and secretion rates; turnover of triglyceride in very low density lipoproteins (VLDL); and turnover of apoprotein B in VLDL and low density lipoprotein (LDL). Studies are designed to determine whether reduction in plasma lipids during treatment is due to a decreased input or an increased removal of lipoproteins. Also, a correlation will be made between turnover of apoproteins of lipoproteins and cholesterol production.